per-dĭŭturnus, a, um, adj.,
that lasts a very long time , very lingering or protracted (rare but class.), Cic. N. D. 2, 33, 85 (but Cic. Sest. 27, 58 Halm and B. and K. read diuturnum).
per-diuturnus adj., lasting very long. ...
An Elementary Latin Dictionary